This invention relates to a roller type toner feeding device for an electrophotographic copying machine.
Accompanying FIG. 1 shows a conventional toner feeding device. It is seen that the device comprises a toner box 2 having a toner outlet port 1 formed at the bottom, a roller 3 formed of a porous elastic material and housed in the toner box 2 in a manner to close the toner outlet port 1, and a toner catching plate 4 extending upward from below the roller 3 to bite the surface region of the foller 3. Particles of toner 5 housed in the toner box 2 enter the pores of the porous elastic roller 3 and are transferred to the toner outlet port 1 in accordance with rotation of the roller 3. Upon reaching the toner outlet port 1, the toner is caught by the toner catching plate 4 biting the roller 3 so as to feed the toner into a developing device (not shown). The roller is rotated in clockwise direction. In the conventional device shown in FIG. 1 the toner feeding rate is controlled by suitably adjusting the angle of rotation of the roller 3. A serious difficulty accompanying the above-mentioned technique of controlling the toner feeding rate is that the rotation angle of the roller must be manually adjusted every time a single copy is reproduced. Otherwise, it is impossible to supply a proper amount of toner in reproducing succeeding copies, failing to obtain clear copies.
In order to overcome the difficulty mentioned above, it has been proposed to make the toner catching plate 4 movable so that the biting degree of the toner catching plate into the elastic roller 3 may be adjusted for controlling the toner feeding rate. This idea is certainly interesting. But, the toner catching plate 4 employed in the conventional device has a smooth upper plane 6 as shown in FIG. 2. In this case, a sharp change is caused in the toner feeding rate where the biting amount of the toner catching plate into the roller varies within a very narrow range of 0 to 0.5 mm as shown in FIG. 3. In addition, the toner feeding rate remains substantially constant if the biting amount mentioned exceeds 0.5 mm. Naturally, an extremely high precision is required for manufacturing and mounting the roller and the toner catching plate. In addition, the operator must adjust very accurately the biting amount of the toner catching plate into the roller for controlling the feeding rate satisfactorily.